Electrical inductive and resistance heating device



I Patented May 19, 1931 UNITED STATES PATENT OFFICE I EMII: FENDT ANDKARL $036M, OF FRANKI'ORT-ON-THE-KAIN-KOGHST, GERMANY,

ASSIGNORS TO I. G. FABBENINDUSTB-IE AKTIENGESELLSCHAIT, OF ERANKFOBT-QN-THE-MAIN, GERMANY ELECTRICAL INDUCTIVE AND RESISTANCE HEATING DEVICENo Drawing. Application filed December 19, 1928,8eria1 No. 415,346, andin Germany December 28, 1928.

The present invention relates to aheatresisting electrical coil and toelectrical resistance heating devices.

The windings ofelectrical indiiction ap- 5 paratus are in some casesliable to be exposed to a temperature which is so high that normalinsulating materials, such as cotton, paper or the like cannot be used.The wires have therefore been taped with as- .10 bestos which, however,at high temperatures,

at about 300 C. loses its mechanical strength and begins todisintegrate. It has been tried to prevent this by impregnating theasbestos band with water glass, but this means also failed attemperatures of about 450 C. be'-- cause the insulation was apt to fuse,causing a short-circuit.

According to this invention temperatures of about 750C. can be attainedinelectrical 2o resistance windings, as well as in induction coils,without causing a loss in mechanical and electrical strength of theinsulation by impregnating the winding, which has been insulated withasbestos or a similar fibrous material, with a cement-masssubstantially.

with the cement-mass. The finished coil is caused to harden for somehours at a normal temperature (about 20 C. to {(1); 1t is 40 then driedfor sometime, dependlng upon the thickness, at about 200 C. untilthewater is completely expelled. In case the coil has to be used attemperatures above 400 C. it has been found suitable to boil it, afterit v i has been hardened for about 20 hours, in

ordinary water in order to remove the resia layer of asbestos which hasbeen likewise impregnated with the cement-mass.

In making heating plates in particular,

the resistance winding is often directly pressed into the clayey mass.Cement-masses containing silicofluorides are also very suitable for thiskind of construction. The resistance material is introduced into thecement-mass which has been stirred to a paste. The further treatment isas described above.

We claim:

1. A heat-resisting electrical coil consisting of a layer of aninsulating fibrgus material, said insulating layer being impregnatedwith a cementitious substance containing a silicofluoride and anelectrical conductor embedded in said layer. v

2. A heat-resisting electrical coil consisting of a layer of asbestos,said layer being impregnated with a cementitious substance containinga-silicofiuoride and an electrical conductor embedded in said layer.

3. An electrical resistance heatin device comprising a body to beheated,'a yer of insulating cementitious material surrounding at leastpart of said body and a resistance coil of an electrically conductivematerial,

embedded in said insulating cementitious material, said insulatingcementitious material being characterized by the presence of asilicofluoride therein.

4. An electrical resistance heath? device com irising a body to beheated, a ayer of insu ating cementitious material surrounding at leastpart of said body, and a-resistance coil consisting of anelectricallyconductive material and a layer of insulating fibrous materialsurrounding said conductive material, said insulating material and saidcementitious material being characterized by the presence of asilicofluoride therein.

In testimony whereof, we aifix our signatures.

EMIL FENDT. KARL SGHORG.

